feat: add Accept: text/markdown content negotiation for agent compatibility

Intercepts requests with Accept: text/markdown at endpoint level (before
the router's :accepts plug rejects them) and returns hardcoded markdown
representations for /, /privacy, and /terms.

lib/towerops_web/endpoint.ex

@@ -117,5 +117,6 @@ defmodule ToweropsWeb.Endpoint do
     plug Phoenix.Ecto.SQL.Sandbox
   end
 
+  plug ToweropsWeb.Plugs.MarkdownNegotiation
   plug ToweropsWeb.Router
 end

lib/towerops_web/plugs/markdown_negotiation.ex

@@ -0,0 +1,61 @@
+defmodule ToweropsWeb.Plugs.MarkdownNegotiation do
+  @moduledoc false
+
+  import Plug.Conn
+
+  @markdown_content %{
+    "/" => """
+    # TowerOps
+
+    Network monitoring and alerting platform built for WISP and ISP operators.
+
+    See the business impact of every network event.
+
+    ## Features
+
+    - Real-time network monitoring
+    - Subscriber impact analysis
+    - Revenue impact tracking
+    - Equipment management
+    - Multi-site support
+
+    ## Get Started
+
+    - [Register](/users/register)
+    - [Log In](/users/log_in)
+    - [API Documentation](/docs/api)
+    - [Privacy Policy](/privacy)
+    - [Terms of Service](/terms)
+    """,
+    "/privacy" =>
+      "# Privacy Policy\n\nVisit [towerops.net/privacy](https://towerops.net/privacy) for the full privacy policy.\n",
+    "/terms" =>
+      "# Terms of Service\n\nVisit [towerops.net/terms](https://towerops.net/terms) for the full terms of service.\n"
+  }
+
+  def init(opts), do: opts
+
+  def call(conn, _opts) do
+    if accepts_markdown?(conn) do
+      case Map.get(@markdown_content, conn.request_path) do
+        nil -> conn
+        markdown -> send_markdown(conn, markdown)
+      end
+    else
+      conn
+    end
+  end
+
+  defp accepts_markdown?(conn) do
+    conn
+    |> get_req_header("accept")
+    |> Enum.any?(&String.contains?(&1, "text/markdown"))
+  end
+
+  defp send_markdown(conn, content) do
+    conn
+    |> put_resp_content_type("text/markdown")
+    |> send_resp(200, content)
+    |> halt()
+  end
+end

test/towerops_web/controllers/page_controller_test.exs

@@ -65,4 +65,18 @@ defmodule ToweropsWeb.PageControllerTest do
 
     assert response =~ "Terms of Service"
   end
+
+  describe "GET / with Accept: text/markdown" do
+    test "returns markdown content when markdown is requested", %{conn: conn} do
+      conn =
+        conn
+        |> put_req_header("accept", "text/markdown")
+        |> get(~p"/")
+
+      assert response(conn, 200)
+      assert get_resp_header(conn, "content-type") == ["text/markdown; charset=utf-8"]
+      body = response(conn, 200)
+      assert body =~ "# TowerOps"
+    end
+  end
 end